Check out Spector Off-road’s web site. They have a nice drawing of a factory shackle with dimensions. The factory shackles pins are 15mm, after market pins are usually 9/16 or 5/8. You need to get bushings w/ the correct inner id. for the shackle pins that you are using.
Right now I run 5/8 grade 8 bolts (5inch long, I think) with nylon lock bolts. They have worked well, although I do frequently lubricate and check for looseness.